This invention relates to a socket having a contact element which in connection with the insertion and installation of an IC package with a prescribed electrical part and IC chip is electrically contacted with this electrical part.
In recent years, the IC package has become thin and small thereby making it more suitable for surface mounting. As the IC becomes thinner and smaller, the quality of the product and any test to determine defective products assumes as important a role as ever.
The testing of the IC packages including the IC for surface mounting typically uses a burn-in test for heat resistance which is carried out by putting the IC package in a heating furnace. A prior art socket for IC package mounting in such a test is shown in FIG. 25.
As shown in an expanded plane view in FIG. 21, an expanded front view in FIG. 22 and an expanded back view in FIG. 23, the IC package 10 has a lead 10b only on one side of the IC chip to be vertically mounted on a printed substrate in a so-called vertical surface mount package (VPAK) type. Protrusions 10a are provided at both ends of the side where the lead 10b of the IC package is provided, with tips 10c of the leads being bent by approximately 90 degrees. FIG. 24 is an expanded cross-section cut along line 24--24 in FIG. 22 which shows this feature. The IC package 10 is mounted vertically on the printed substrate 50 which is indicated by an imaginary line. In this state of mounting, the protrusions 10a are inserted into blind holes 50a of the printed substrate 50, with the result that the IC package 10 is positioned relative to the printed substrate 50 and the bent tip 10c of the lead 10b is soldered to the wiring 50b of the printed substrate 50.
In connection with a burn-in test, however, the IC package 10 is mounted horizontally on the socket as shown in FIG. 25. FIG. 25 shows an expanded cross-section of a socket with the IC package having been mounted. The socket comprises a main socket body or base 41 equipped with a contact 43 and a cover 42. The cover is biased open by a coil spring 45 and is stopped at a prescribed location as compared with the base by a "stop" mechanism which is not shown in the drawings.
The charging of IC package 10 is done by inserting the package into space 41a placing it on the surface 41c of the stand 41b. The contact 43 has its basal part 43a buried in the bottom wall of the base 41 and a terminal part 41e that protrudes from the bottom of the base 41. A pin part 43b is attached to the base part 43a and has a curved part extending into a space in the base but further with a tip portion 43c and tip end 43d. Due to the elasticity of pin part 43c, the tip 43d of the tip part 43c compressively contacts the curved tip portion 10c of the lead 10b upon the insertion of the IC package 10 thereby providing electrical contact between lead 10b and contact 43.
As shown in FIG. 26, the electrical connection between lead 10b and contact 43 is made certain by the use of a sharp contact tip end 43d which bites into the tin plated layer through the oxidized coating 10f on the surface of the tin plated layer. If tip end 43d bites through the tin plated layer 10e of the lead 10b in the core material 10d (nickel or copper), good electrical connection is still maintained. The reason for this good electrical connection lies in minimizing the contact resistance due to the oxide coating 10f that is inevitably produced on the surface of the tin plated layer by biting through the oxide layer. This socket, however, of the aforementioned construction still has the following problems:
(i) The surface of the contact is often plated with gold, etc., for low contact resistance and good corrosion resistance and the tin on the surface of the lead adheres to the surface of the plated layer on the contact surface during connection of the contact and lead. As a consequence of this fact, the contact resistance increases at the time of a burn-in test and the reliability of the test will then drop.
(ii) Since the lead is only on one side of the IC package, the IC package tends to jump upward as it is pushed by the contact.
(iii) In view of the fact that the contact is arranged outside as compared with the IC package, the width of the socket becomes greater by the width of the contact, with a result that the density of the mounting on the printed substrate for test in the case of a large number of sockets with the IC package mounted drops at the time of a burn-in test. Because of this fact, there is a decrease in the number of IC packages that can be tested at one time, thereby bringing about inefficiency.
The aforementioned problem (i) similarly exists in the case of the IC package with the leads being provided on a plurality of sides such as the IC package of the type where leads are provided on the mutually opposed sides in addition to the IC package of the VPAK type.